Children from bilingual homes are a large and growing segment of the population. Their early language competencies are neither well described nor understood. Because language skills during the preschool years are predictive of later academic achievement and social adjustment, the current poor understanding of early bilingual development constitutes a significant public health problem. Aim 1 of the proposed research is to identify the environmental factors associated with successful bilingual development in children exposed to two languages from infancy. The language skills and language environments of 2 1/2 -year-old Spanish-English bilingual children will be assessed, and the relation of their language skills to their language environments investigated. The proposed research will be the first to describe young bilingual children's language competencies in terms of their phonological, lexical, and morphosyntactic development in both languages, assessed with standardized instruments and with measures based on spontaneous speech samples. The proposed research will be the first to describe bilingual environments using caregiver interviews, caregiver-kept diaries of their children's language experience, and samples of caregivers'child-directed speech in both languages. The approaches to describing children's language competencies and language environments will make use of variable-centered and person-centered data analytic techniques, yielding descriptions in terms of continuous dimensions of variability and in terms of frequently-occurring types, or categories. Analyses of the relations between skills and environments will be conducted using both kinds of descriptors. Aim 2 of the proposed research is to test theory-driven hypotheses regarding mechanisms of language development against the evidence of within- and across-language interrelations among components of language skill in bilingual children. Bilingual children may show patterns of development in which phonological and morphosyntactic development are more advanced than lexical development and in which receptive competence is more advanced than productive competence, relative to monolingual norms. In such bilingual children, the interrelations among skills across domains should differ from those typically observed, and the specifics of those interrcorrelations should constrain hypotheses regarding the mechanisms of language acquisition and suggest ways in which growing knowledge of two languages does or does not interact in the process of bilingual development. The proposed research will fill a gap in the knowledge base needed to provide quality educational and clinical services to a substantial segment of the nation's children and will advance scientific understanding of the process of early bilingual development. PUBLIC HEALTH RELEVANCE: The current lack of information about the language skills of children growing up in bilingual homes is an obstacle to maximizing the economic potential of a substantial segment of the nation's children. The aims of the proposed research are to describe the patterns of bilingual competencies that children display and to identify environmental correlates of successful bilingualism at an early, critical juncture in children's development.